Method to product microcellulose
The present invention relates to a process for producing microcellulose comprising hydrolyzing fibrous cellulosic material with an acid at an elevated temperature or acidifying fibrous cellulosic material followed by washing and hydrolyzing the washed cellulosic material at an elevated temperature to produce a microcellulose-hydrolysate mixture followed by separation of the microcellulose from the hydrolysate, wherein the mixture or separated hydrolysate or microcellulose is optionally neutralized, and wherein the microcellulose production is integrated to production of a pulp mill such that at least part of chemicals used in the acidification, acid hydrolysis and/or neutralization is produced by an integrated chemical recovery process of the pulp mill.
1. A process for producing microcellulose comprising
i) hydrolyzing fibrous cellulosic material comprising bleached or unbleached pulp made from softwoods or hardwoods with an acid comprising sodium bisulphate and/or sodium bisulfite at an elevated temperature, wherein the amount of acid is from 0.2 to 2% on dry weight of the cellulose, or
ii) acidifying fibrous cellulosic material comprising bleached or unbleached pulp made from softwoods or hardwoods with an acid comprising sodium bisulphate and/or sodium bisulfite followed by washing and hydrolyzing the washed cellulosic material at an elevated temperature,
to produce a microcellulose-hydrolysate mixture followed by separation of the microcellulose from the hydrolysate, wherein the mixture or separated hydrolysate or microcellulose is optionally neutralized, and wherein the microcellulose production is integrated to production of a pulp mill such that at least part of the sodium bisulphate and/or sodium bisulfite used in the acidification and/or acid hydrolysis or at least part of the sodium bisulphate and/or sodium bisulfite used in the acidification and/or acid hydrolysis and chemicals used in the neutralization are produced by an integrated chemical recovery process of the pulp mill, wherein the hydrolysis is carried out in a continuous bleaching tower, and wherein the produced microcellulose having an average particle size of 8-100 μm is obtained without a mechanical treatment.
2. The process according to claim 1 , wherein the cellulosic material is acidified in step ii) to a pH value of 4 or below 4.
3. The process according to claim 1 , wherein the sodium bisulfate is obtained by converting sulphur dioxide in flue gases of the pulp mill to sodium bisulfite in a bisulfite scrubber and further to sodium bisulfate by means of an oxidant.
4. The process according to claim 1 , wherein the sodium bisulfite is obtained by converting sulfur dioxide in flue gases of the pulp mill to sodium bisulfite in a bisulfite scrubber.
5. The process according to claim 1 wherein the neutralization of microcellulose-hydrolysate mixture or hydrolysate or microcellulose is carried out by sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide or magnesium hydroxide.
6. The process according to claim 1 , wherein the neutralization of microcellulose-hydrolysate mixture or hydrolysate or microcellulose is carried out by sodium carbonate or sodium bicarbonate wherein at least part is produced in the integrated chemical recovery process of pulp mill.
7. The process according to claim 1 , wherein separated hydrolysate or neutralized hydrolysate is at least partly returned to the integrated chemical recovery process of pulp mill for producing energy.
8. The process according to claim 1 , wherein the hydrolysis takes place at a temperature of at least 80° C.
9. The process according to claim 1 , wherein the consistency of the cellulose in the hydrolysis is from 3 to 50% on dry weight of the cellulose.
10. The process according to claim 1 , wherein the hydrolysis time is from 5 to 240 minutes.
11. The process according to claim 1 , wherein mechanical energy input during the hydrolysis is carried out to ensure even chemical and temperature distribution and without mechanical cutting, and defibration of the cellulose matrix, at most 20 kWh per dry ton cellulose.
12. The process according to claim 1 , wherein the fibrous cellulosic material and the acid are mixed with each other.
13. The process according to claim 1 , wherein the fibrous cellulosic material has a lignin content of below 100 kappa number.
14. The process according to claim 1 , wherein the amount of acid in the acid hydrolysis i) is from 0.5 to 1.5% on dry weight of the cellulose.
15. The process according to claim 1 , wherein the cellulosic material is acidified in step ii) to a pH value of 3 or below 3.
16. The process according to claim 1 , wherein the cellulosic material is acidified in step ii) to a pH value between 1.5 and 2.5.
17. The process according to claim 1 wherein the acid hydrolysis or acidification is carried out with sulphuric acid, sodium bisulphate, sodium bisulfite, hydrochloric acid or nitric acid.
18. The process according to claim 1 , wherein the acid hydrolysis or acidification is carried out with sodium bisulphate and/or sodium bisulfite wherein at least part is produced in the integrated chemical recovery process of a kraft pulp mill.
19. The process according to claim 1 , wherein the hydrolysis takes place at a temperature of at least 100° C.
20. The process according to claim 1 , wherein the hydrolysis takes place at a temperature between 100 and 185° C.
21. The process according to claim 1 , wherein the hydrolysis takes place at a temperature between 120 and 180° C.
22. The process according to claim 1 , wherein the hydrolysis takes place at a temperature between 120 and 160° C.
23. The process according to claim 1 , wherein the consistency of the cellulose in the hydrolysis is from 8 to 50% on dry weight of the cellulose.
24. The process according to claim 1 , wherein the consistency of the cellulose in the hydrolysis is from 15 to 50% on dry weight of the cellulose.
25. The process according to claim 1 , wherein the consistency of the cellulose in the hydrolysis is from 20 to 50% on dry weight of the cellulose.
26. The process according to claim 1 , wherein the consistency of the cellulose in the hydrolysis is from 25 to 45% on dry weight of the cellulose.
27. The process according to claim 1 , wherein the hydrolysis time is from 5 to 180 minutes.
28. The process according to claim 1 , wherein the hydrolysis time is from 15 to 150 minutes.
29. The process according to claim 1 , wherein mechanical energy input during the hydrolysis is carried out to ensure even chemical and temperature distribution and without mechanical cutting and defibration of the cellulose matrix at most 10 kWh per dry ton cellulose.
30. The process according to claim 1 , wherein mechanical energy input during the hydrolysis is carried out to ensure even chemical and temperature distribution and without mechanical cutting and defibration of the cellulose matrix between 1 and 5 kWh per dry ton cellulose.
31. The process according to claim 1 , wherein the fibrous cellulosic material comprises kraft pulp, soda-AQ pulp, sulfite pulp, neutral sulfite pulp, acid sulfite pulp or organosolv pulp.
32. The process according to claim 1 , wherein the fibrous cellulosic material is kraft pulp.
33. The process according to claim 1 , wherein the fibrous cellulosic material has a lignin content of below 40 kappa number.
34. The process according to claim 1 , wherein the fibrous cellulosic material has a lignin content of below 30 kappa number.
35. The process according to claim 1 , wherein the fibrous cellulosic material has a lignin content of below 10 kappa number.
36. The process according to claim 1 , wherein the produced microcellulose has an average particle size of 10-60 μm.
37. The process according to claim 1 , wherein the produced microcellulose has particle size distribution at least 90% by volume of the particles have a size of below 100 μm.